Radionuclide Distribution and Hydrochemical Controls in Groundwater of the Nile Valley, Upper Egypt: Health and Environmental Implications

This study provides a comprehensive evaluation of naturally occurring radionuclides—radium-226 (226Ra), thorium-232 (232Th), and potassium-40 (40K)—in groundwater systems across the Nile Valley regions of Upper Egypt, based on the analysis of 85 groundwater wells. Measured mean activity concentrations were 0.74 ± 0.3 Bq/L for 226Ra, 0.24 ± 0.1 Bq/L for 232Th, and 13 ± 4 Bq/L for 40K, with 226Ra displaying low correlations with salinity indicators including chloride (Cl−), sodium (Na+), electrical conductivity (EC), and total dissolved solids (TDS). Notably, approximately 30% of sampled wells exceeded the World Health Organization (WHO) guidance level of 1 Bq/L for 226Ra, primarily in central and eastern zones influenced by elevated salinity and evaporite dissolution processes. Geospatial mapping combined with multivariate statistical analysis identified four principal components accounting for over 85% of total data variability, demonstrating that depth-dependent processes, including prolonged water–rock interaction and redox evolution, are the primary controls on 226Ra mobilization, with salinity-driven ion exchange as a secondary factor. Minor anthropogenic influences, potentially linked to agricultural activities in shallow aquifers, were also detected. Radiological risk assessment confirmed that calculated annual effective doses remain well within international safety limits (<1 mSv/year), although infants and children demonstrated relatively higher exposure levels due to increased water intake per unit body weight. Lifetime cancer risk estimates via ingestion pathways yielded values below 1 × 10−4, aligning with global health organization benchmarks and reinforcing the general safety of groundwater use in the region. The study highlights potential risks posed by saline groundwater to ancient monuments and archaeological sites, as the cycles of salt forming and breaking down might speed up damage to buildings made of limestone and sandstone. These findings establish a robust scientific foundation for future groundwater quality management and cultural heritage conservation efforts in the Nile Valley region of southern Egypt.